1. Field of the Invention
The present invention relates to an optical disk read only memory. More particularly, the present invention relates to a technique which allows adding unique information, etc., individually to an optical disk read only memory that is mass-produced by pit transfer.
2. Description of the Related Art
In an optical disk read only memory, for example, a ROM (Read Only Memory)-type CD (Compact Disc), DVD (Digital Versatile Disc), BD (Blu-ray Disc: registered trademark), HD-DVD (High Definition DVD), etc., information data of music, video, application programs, and the others is recorded in an area called a content area by a predetermined recording modulation method.
For example, these playback-only optical discs are used by a large number of content holders as content providing means because of the low production cost brought about by the excellent mass-productivity of the discs.
By taking a DVD as an example, a production process of a playback-only optical disc will be described. The production process of a playback-only optical disc roughly includes three processes: a mastering process in which a master of an optical disc is produced using a laser beam; a molding and film-forming process in which a large number of disc substrates are produced using a stamper created from the optical disc master, and a film is formed on each of the disc substrates; and a bonding process in which two optical discs, each of which having a thickness of 0.6 mm to make a pair, are bonded together by adhesive having a predetermined thickness to be a DVD disc medium having a thickness of 1.2 mm.
In the above-described molding and film-forming process, the disc substrates, which are mass-produced using a stamper, are produced by transferring a concave-convex pattern formed on the stamper. That is to say, a recording data string based on pits/lands is formed on a portion to be an information-recording surface as the concave-convex pattern. The recording data string is formed in a spiral or concentric recording track. Then, the information-recording surface, on which pits/lands are formed as a concave-convex pattern, is covered with a metal-alloy reflective film.
After the completion of the disc, laser light emitted from a playback apparatus is reflected by the pits/lands portion. In this regard, a land portion between pits in a pit string is also called a “space”.